This project is aimed at attaining a detailed understanding of the structural and functional relationships of photoreceptors and their visual pigment content pertaining to photic excitation. Topics of current study are: 1) Spectroscopic chracterization of vertebrate visual pigments in situ. 2) Description of photoreceptors for visual pigment content, receptor mosaic, habitat, and evolutionary trends in bony fishes. 3) Theoretical and experimental study of the band structure of the absorption spectra in visual pigments and related molecules. 4) Bleaching kinetics studies in solubilized visual pigments from the viewpoint of solvent effects. 5) Chemical probing of the micro-environment of the visual pigment chromophore in cells and in solubilized pigments with dissolved dyes and organic molecules. BIBLIOGRAPHIC REFERENCES: Shichi, H., Harosi, F.I., Kawamura, S. and Yoshizawa, T.: Isolation of three isochromic forms of rhodopsin which show different bleaching kinetics. Biophys. J. 17: 79a, 1977. Shichi, H., Muellenberg, C.G., Harosi, F.I. and Somers, R.L.: Isolation of three isochromic forms of rhodopsin in digitonin. Vision Res. 17: 633-636, 1977.